The pitch at the Riverside Ground again offered steep bounce in the morning, but Durham's depleted attack was unable to turn the screw as Graham Rose (48) and Rob Turner (65) led the fightback with a sixth-wicket stand of 80.
Caddick, whose previous best was an unbeaten 58 against Sussex last year, hit seven fours and one six, and shared a last wicket stand of 62 with the other Somerset fast bowler who has been absent for most of the season, Andre van Troost.
Alan Wells, left out by England at Trent Bridge, made sure his name receives full consideration for the final Test with his sixth Championship century of the season. He came in with his side at 22 for 2 against Worcestershire and his 108 included 18 fours. Keith Greenfield fell to Phil Newport, who finished with 5 for 66, one short of a century having hit the same number of fours as his captain and a six.
Adrian Rollins batted all day for 129 as Derbyshire made 336 for 4 against Gloucestershire at Bristol. It was his second Championship hundred, beating his 118 against Glamorgan two matches ago.
He hit 19 boundaries and he shared two century stands. Kim Barnett's 68 took him to exactly 1,000 runs for the season as he put on 106 for the first wicket and 107 with Chris Adams, also 68, for the second.Reuse content